Method of treating alloys



Patented July 9, 1940 UNITED STATES METHOD OF TREATING ALLOYS Joseph H. Brennan, Niagara Falls, N. Y., assignor to Electro Metallurgical Company, a corporation of West Virginia No Drawing. Application January 21, 1939, Serial No. 252,070

2 Claims.

For the production of various useful alloys there is a demand for master alloys containing no more than the commercially practicable min imum of carbon. Such master alloys include those containing one or more of the elements manganese, vanadium, titanium, chromium, and zirconium, usually with some iron or, less frequently, with nickel or copper.

One method of producing master alloys of this kind involves the reaction of an ore or an oxydic compound with a low-carbon silicide or high silicon alloy, for instance ferro-silicon or silicomanganese, whereby the silicon is eliminated without introducing any substantial further amount of carbon. In such methods, the carbon content of the product is determined almost entirely by the carbon content of the silicide or high-silicon alloy. Accordingly, it is important that silicides and high-silicon alloys containing the lowest possible percentages of carbon be made available at a reasonable cost, and such is the principal object of this invention.

The usual commercial methods of making silicides and high-silicon alloys yield products containing small but substantial amounts of carbon, from say 0.1% to 1% or more. One well known method comprises the simultaneous reduction of ore and silica with carbon in an electric furnace, the silicon thereby introduced into the product being relied upon to minimize the contamination of the product by carbon derived from that in the original furnace charge. Usually, the ingredients of the charge are so proportioned that the product contains about 40% to 551% silicon, al- 35 though on occasion the proportion of this element may be as low as 15% or 20% or as high as 60% v. silicon products contain substantial amounts of carbon.

I have observed that a very substantial part of the carbon in alloys of this description exists as silicon carbide, and I have discovered that all but the slightest traces of this silicon carbide can be removed by a relatively simple treatment.

The invention has many advantages including the ability consistently to produce material of extremely low carbon content from material containing even large amounts of silicon carbide.

According to the invention, a bath of the molten silicide or high-silicon alloy is maintained molten in the presence of a molten slag having a property of dissolving or trapping silicon carbide. Molten slag may be added to molten alloy as the latter comes from the furnace, or the alloy and slag may suitably be heated in, an electric furnace, preferably as a shallow pool to permit ready and rapid exposure of all portions of the pool to the slag. The treatment may be continued until 5 substantially all of the silicon carbide enters the slag, and the slag may then be separated from the silicide or alloy.

Almost any slag may be used which is fairly fluid at temperatures in the neighborhood of the -10 melting point of the alloys, which is not too heavily charged with silicon carbide, which does not severely attack the furnace lining, and which does not too rapidly oxidize the valuable constituents of the alloy. Slags of the following re- 15 spective approximate analyses have been used successfully and are disclosed as typical examples:

(1) 49.4% S102, 18.2% A1203, 21.6% CaO, 9.6% MgO, with an acid-to-base ratio of 1.6;

(2) 33.4% SiOz, 27.0% A1203, 23.8% CaO, 15.6%

MgO, with an acid-to-base ratio of 1.0.

The proportion of slag to metal is not critical.

A satisfactory ratio that is suggested as 'an ex- 25 ample is one part of slag to ten parts of metal, by weight. Such a proportion of slag is adequate without unduly burdening the furnace with an excess volume of slag.

Nor is the time of treatment critical. The op- 30 timum time will depend upon the design of the furnace, the compositions of the various materials involved, and upon various other factors. It has been found that about 45 to 60 minutes is adequate for the treatment of 5000 pounds of molten metal with 500 pounds of slag in an open are electric furnace of the tilting type widely used for making steel.

In extensive tests of the method of the invention, numerous batches of alloy containing 40 about to silicon and 0.17% to 2% carbon were treated as just described. In each case the carbon content of the product was no greater than 0.03%, in most instances it was substantially less than 0.03%, and in a few instances it was less 5 than 0.01%.

Although the treatment of alloy containing about 45% to 50% silicon has been emphasized herein, this is only an illustrative and preferred molten mass of said alloy or silicide in contact with a slag until practically all of said silicon carbide has entered said slag.

2. Method of treating metallic silicide, or alloy comprising a. large proportion of silicon, contain- 7 ing a small but substantial proportion of carbon as silicon carbide which comprises heating a shal- JOSEPH H. BRENNAN. 

